With a high-density optical disc drive, although it is necessary to correct spherical aberrations which depend on a disc substrate thickness error, operation of an aberrations correction element takes time and therefore easy correction according to a disc radius degrades the operability of the apparatus. TPCDs include, but are not limited to, miniplasmin, microplasmin and derivatives and variants thereof. The generator rotor being mechanically coupled to the exciter rotor and disposed for rotation within the generator stator, wherein the poles of the stators, or the poles of the rotors, are angularly displace by one pole pitch. The dosing mechanism is configured to move in relation to the first and second arms so as to close over at least one of the first and second arms to cause the distal ends of the arms to come together.